Back in my roadie days of doing PA for some rather major acts, before the days of three way active crossovers, we used to use Electrovoice tweeter protectors. Unlike fuses which don't recover when they blow, the EV devices did. It was a simple circuit which consisted of a capacitor, diode, and N.C. reed relay. The way it worked was when the high frequency level exceeded a certain voltage, the relay opened and stayed open until the level (voltage) was decreased. We hardly ever had blown H.F. drivers. The downside is (with PA anyway), that usually your high frequency levels were exceeded across the board, and all the tweeter protectors kicked in around the same time. Depending on the music, one could hear the high end drop system wide around the same time. That was the signal for whomever was mixing house to either change the EQ, or back off the throttle a little.
